Ethylene glycol and propylene glycol are valuable materials with a multitude of commercial applications, e.g. as heat transfer media, antifreeze, and precursors to polymers, such as PET. Ethylene and propylene glycols are currently made on an industrial scale by hydrolysis of the corresponding alkylene oxides, which are the oxidation products of ethylene and propylene, produced from fossil fuels.
In recent years, increased efforts have focussed on producing glycols from renewable feedstocks, such as sugar-based materials. The conversion of sugars to glycols can be seen as an efficient use of the starting materials with the oxygen atoms remaining intact in the desired product.
Current methods for the conversion of saccharides to sugars revolve around a hydrogenation/hydrogenolysis process as described in Angew. Chem. Int. Ed. 2008, 47, 8510-8513. Continuous processes for generating at least one polyol from a saccharide-containing feedstock are described in WO 2013/015955 and CN 103731258A. A process for the co-production of bio-fuels and glycols is described in WO 2012/174087.
An important aim in this area is the provision of a process that is high yielding in desirable products, such as ethylene glycol and propylene glycol, and that can be carried out on a scale that makes it industrially viable. A key consideration, therefore, is the level of dilution of the catalytic process. Carrying out the process at high levels of dilution can lead to inefficiencies and will add to the difficulties in separating the desired products.
Although acceptable conversion levels to the desired products are now possible for the catalytic conversion of saccharides to glycols, these are generally achieved at low concentrations of saccharides in the catalytic reactors. In general, the use of higher concentrations of saccharides leads to reduced overall yields.
It would be desirable, therefore, to provide a process for the catalytic conversion of saccharides to glycols in which higher concentrations of saccharides can be used while maintaining acceptable yields of the desirable glycols.